Although gastrin is a medically important hormone that has been well studied with regard to structure and physiology, very little is known about the molecular mechanisms which regulate its synthesis. The main objective of the proposed research is to further our understanding of the molecular events controlling the metabolism and biosynthesis of gastrin in Zollinger-Ellison and X-ray-induced islet cell tumors by examining the regulation of expression of gastrin-specific genes. Studies of gene expression in these tumor tissues will also serve to probe the events surrounding uncontrolled cell growth as occurs in malignancy. Specifically we will extract the total RNA pool from the above tumor tissues by procedures currently in use, and will isolate mRNA from the total RNA by chromatography on oligo dT cellulose. For detection, isolation and nucleotide sequence analysis of gastrin mRNA, we propose to use a chemically synthesized oligodeoxynucleotide as a specific probe. The nucleotide sequence of the probe will be predicted from the known amino acid sequence of gastrin. The synthetic oligodeoxynucleotide will be used: (1) as a hybridization probe in assays for gastrin mRNA during conventional mRNA isolation procedures; (2) as a specific primer in the template (mRNA) directed synthesis of complementary DNAs; and (3) as a ligand in affinity chromatographic procedures for the isolation of homogeneous gastrin mRNAs. The physical properties of the isolated mRNAs will be studied and nucleotide sequence analysis will be carried out to identify the coding and non-coding regions of the messages. cDNAS syntehsized from mRNA and gene(s) coding for gastrin will be amplified in suitable bacterial plasmids. In addition, the initial translation products synthesized in the wheat germ ribosomal system will be isolated and characterized. These translational studies will provide information on the probable size of the initial in vivo transcript of the hormone and may eliminate controversy over the existence of the "big-big" gastrin.